Such circuit arrangements are needed, for example, if signal channels which carry signals originating from several measuring points with suitable sensors are to be alternately or successively connected to the input of a differential amplifier. Each signal channel generally has a signal line and a channel zero line.
The channel zero line need not necessarily be connected to ground, as in the case of a battery, for example, where the signal line and the channel zero line serve to connect the two terminals of the battery to desired points of a circuit.
Normally, the multiplexer serves to connect both the signal line and the channel zero line to the differential amplifier; thus, a two-terminal through-connection is made.